1. Field of the Invention
Systems and methods consistent with the present invention relate to wireless transmitting/receiving data in a wireless network, and more particularly, to a wireless network system and a method of transmitting/receiving data in the wireless network system, in which a period of a super frame for transmission/reception of a packet for request and approval of bandwidth allocation in the network is separately set and data are then transmitted/received through the allocated bandwidth.
2. Description of the Related Art
FIG. 1 is a view illustrating a half-duplex wireless network using related art Request-To-Send (RTS) signals and Clear-To-Send (CTS) signals.
In general, a wireless network uses a half-duplex scheme by which it is impossible to simultaneously perform transmission and reception, and an RTS signal 111 and a CTS signal 121 are used in order to prevent collision due to media occupation during access of wireless media using the half-duplex scheme.
A transmitting station 110 including a frame to be sent, first starts the transmission process by transmitting the RTS signal 111, all neighboring stations which have received the RTS signal 111 stop generating radio waves. When a receiving station 120 receives the RTS signal 111, it responds to the RTS signal 111 by transmitting the CTS signal 121, which also makes all neighboring stations stop generating radio waves. The transmitting station 110 which has received the CTS signal 121 transmits a frame 112 and then receives the acknowledgement signal 122 from the receiving station 120 which has received the frame 112.
Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA), which corresponds to a Media Access Control (MAC) algorithm usually used in a wireless local area network (LAN), is provided by a Distributed Coordination Function (DCF) which, as in Ethernet, identifies whether a wireless link is clear or in use before the transmitting station 110 transmits the frame 112, and which makes use of any back-off at the time of the end of each frame in order to avoid a collision with other stations.
A function of carrier sense is used to decide whether media is available or not, and is classified into a function of physical carrier sensing and a function of a virtual carrier sensing. The function of physical carrier sensing is provided by a physical layer, and depends on an adopted media and a scheme of modulation. The function of a virtual carrier sensing is provided by a Network Allocation Vector (NAV), wherein the NAV refers to a timer which implies the time information in a case where media have been reserved. The NAV is included in and transmitted by the frame header of the RTS signal 111 and the CTS signal 121, and the transmitting station 110 and the receiving station 120 set times, which are necessary to complete their operations, to the NAV to prevent other stations from using the media.
Meanwhile, timing is based on a super frame under the circumstances of a wireless personal area network (PAN).
FIG. 2 is a view illustrating a related art super frame which includes a Beacon Period 210, a Contention Access Period 220, and a Channel Time Allocation Period 230. Asynchronous Data or a control Command is transmitted/received through the Contention Access Period 220. The Channel Time Allocation Period 230 includes a Channel Time Allocation (CTA) 232 and a Management CTA (MCTA) 231. The Control command, Isochronous Data or Asynchronous Data are transmitted/received through the CTA 232.
The length of the Contention Access Period 220 is determined by an access point, and is transmitted to the stations constituting the network through the beacon frames which are distributed to the Beacon Period 210.
The above-mentioned CSMA/CA is used as a media access scheme during the Contention Access Period 220. On the other hand, a Time Division Multiple Access (TDMA) scheme including a specified time window per each station is used during the Channel Time Allocation Period 230. An access point allocates a channel time to a device requesting an access to media, and transmits/receives data to and from the corresponding station during the allocating period. Here, the MCTA 231 is allocated to a pair of stations that intend to transmit/receive data to and from each other to be used to access the TDMA, otherwise, it is used as common CTA that uses a Slotted Aloha protocol.
During data transmission, not only the scheme where compressed data is transmitted with the bandwidth of several gigahertz (GHz), but also the scheme where uncompressed data is transmitted with the bandwidth of scores of GHz is being tried out. The uncompressed data, the volume of which is larger than that of the compressed data, are possible to be transmitted with only scores of GHz-bandwidth, and though there is loss of packets during data transmission, is less affected on the output of the data than the compressed data is.
Here, it is necessary for a transmitting station to request a bandwidth allocation and to receive acknowledgement of approval of bandwidth allocation in order to transmit data, and the transmission can be carried out during the Contention Access Period 220.
That is, the transmitting station should contend with other existing stations in the network for access to media, at this time, if the transmitting station does not receive the approval of a bandwidth allocation via the contention, it has to wait for the next contention period or the next super frame.
It may be inconvenient for a user of a receiving station, who intends to receive the multimedia contents from the transmitting station to regenerate them at real time, to have data reception delay caused by the reasons above. Accordingly, there is a need for a method of operating a contention scheme more reasonably for transmitting/receiving data.